The invention relates to embossing of paper products, for example, paper towels, toilet tissue and napkins, in which an improved embossing combination is used which is particularly suitable for the embossing of paper products made from recycled pulp.
Paper products, such as paper towels, napkins and toilet tissue are widely used on a daily basis for a variety of household needs. Typically, such products are formed of a fibrous elongated web which is either packaged in rolls or in a folded stack. The fibrous webs are usually embossed to increase the bulk of the tissue and to improve the absorbency, softness and appearance of the product both as individual sheets, and in providing a uniform stack or roll package. Embossing can also aid in holding superposed plies of a web together. A commonly used embossing apparatus includes one or more steel embossing rollers having male protuberances thereon for forming the embossed pattern, and a corresponding steel roller which includes matched or mated female recesses which are a three dimensional mirror image of the male protuberances. The web passes between the nip (gap) of the male and female embossing rollers such that the embossed pattern is imparted to the web.
Recently, environmental concerns have led to the use of greater amounts of recycled pulp in the production of paper products. However the economies of recycling make it practically impossible to remove all contaminants from the recycled pulp. In particular, recycled pulp often contains contaminants such as particles of glue and small pieces of plastic which adhere to the pulp, and which are known as xe2x80x9cstickiesxe2x80x9d. These contaminants when passed through the embossing rollers of paper production equipment may adhere to, or become lodged in, the protuberances or recesses of the rollers causing excess wear and possible damage to the embossing rollers, thus negating the savings had from the use of recycled materials. If on the other hand, the clearances embossing machinery are adjusted to accommodate possible contaminants in the recycled pulp, the qualities of the finished paper product may be adversely affected, which will render such recycled pulp based products less commercially attractive.
The present invention is directed to apparatus and methodology to provide embossing of recycled pulp without adversely affecting the processing machinery. This enables the recycled pulp to be embossed in a manner similar to that of non recycled pulp which provides an absorbency, softness and appearance to the finished product which compares favorably to paper products made from non-recycled pulp. It has been found that recycled pulp can be embossed in a manner comparable to that of non-recycled pulp, even if it contains contaminants, if the embossing is carried out by matched embossing rollers in which one of the rollers is relatively soft Shore A (durometer) hardness of 40-65 and the other roller is relatively hard Shore A (durometer) hardness above about 90. The hard roll of the matched set may be a steel roll which is xe2x80x9coffxe2x80x9d of the Shore A hardness scale. As used herein, the terminology having a Shore A hardness of at least about 90 and the like or xe2x80x9cgreater than about 90xe2x80x9d includes harder surfaces such as steel surfaces whether or not a different hardness scale would be applicable. As one of skill in the art will appreciate, a PandJ hardness scale is applicable to steel surfaces. Recycled pulp, even containing contaminants, may be embossed in this manner without causing excess wear or damage to the embossing rollers.
As used herein a matched set of embossing rollers means that the male embossing elements, carried by one roller, are engraved first and the female elements carried by the other rollers are subsequently made from the male elements, or vice versa, so that both elements are virtually inverse or reciprocal images of each other within the practicalities of manufacturing tolerances. This is in contrast to xe2x80x9cnnmatchedxe2x80x9d embossing rollers in which the male and female embossing elements are not identical in shape, but still are positioned relative to each other in registry such that they engage.
It is an object of the present invention to provide apparatus and methodology for embossing webs that will avoid damage to the processing machinery should the web contain contaminating particles.
It is an object of the present invention to provide apparatus and methodology for embossing paper products that will permit processing of recycled pulp without causing excess wear or damage to the processing machinery.
It is an object of the present invention to provide apparatus and methodology for embossing paper products that will permit older embossing machinery having matched embossing rollers to be retrofitted with a matched roller that can accommodate pulp that may contain contaminants, such as recycled pulp.
U.S. Pat. Nos. 5,503,896 and 5,529,563, both to Veith et al., disclose methods for embossing webs using unmatched male and female embossing elements which are preferably made by laser engraving rubber embossing rolls (see, e.g., col. 3, lines 49-52 of U.S. Pat. No. 5,503,896). The male and female embossing elements can be made of different materials. For example, the male elements can be made of steel, and the female elements can be composed of a deformable material, such as rubber, or vice versa (see, e.g., col. 4, lines 3-5 of U.S. Pat. No. 5,503,896). The web can be any web suitable for embossing, including paper, tissue, nonwoven, films, laminates, combinations thereof and the like (see, e.g., col. 4, lines 10-13 of U.S. Pat. No. 5,503,896).
U.S. Pat. No. 5,727,458 to Schulz (the inventor herein) discloses an embossing method wherein two plies of web material are multilevel embossed between rigid engraved embossing rolls and backup embossing rolls. The backup embossing rolls can be composed of laser engraved rubber (see, e.g., col. 3, line 64 and col. 4, lines 56-57 and 67). The non-backup embossing rolls are generally composed of steel but may be substituted with laser-engraved rubber rolls (col. 4, lines 16-21). The backup embossing rolls may have a mirror image engraving of the embossing pattern on the non-backup embossing rolls (col. 4, lines 64-66). The embossing method can be used to make toilet tissue and paper towels (col. 3, lines 53-54).
U.S. Pat. No. 5,269,983 to Schulz (the inventor herein) describes a method of embossing involving a mated pair of resilient and rigid embossing rolls. According to the ""983 patent a laser can be utilized to form recesses in a resilient roll such that the resilient roll receives protuberances of a rigid male embossing roll when the rolls are placed in contact